Traffic detector



May 21, 1940. J. L. BARKER 2,201,146

TRAFFIC DETECTOR Filed Aug. 14, 1937 2 Sheets-Sheet 1 ==x 255s Z IINVENTOR JOHN L. BARKER May 21, 1940. J. 1.. BARKER 2,201,146

TRAFFIC DETECTOR Filed Aug. 14, 1937 2 Sheets-Sheet 2 IN V EN TOR.

JOHN L. DAQKEQ Kiowa 55L ATTORNEY Patented May 21, 1940 UNITED STATESPATENT OFFICE TRAFFIC DETECTOR Application August 14, 1937, Serial No.159,059

24 Claims. (Cl. 171-209) This invention relates to trafiic detectors andmore particularly to detectors of a magnetic type for detecting thepassage of vehicles in streets,

roadways, driveways, doorways, tunnels and the I like as well asarticles passing along conveyors or chutes, and other forms of trafficin these or other trafiic paths, where such trafiic contains magneticmaterial, and the terms tramc, vehicle, and traffic path and the likeused in the specification and claims of this application will beunderstood to include broadly all items and forms of trafiic and pathsof travel of the same. In accordance with the invention the magneticdetector unit itself will provide on passage of traffic a distinctiveelectrical impulse which may actuate a relay or amplifier unit, or otherresponsive device. This invention is primarily concerned with theprovision of an improved detector of this type which will be verysubstantially non-responsive to trafiic units go outside the rangeof thedetector or to magnetic or other electrical disturbances outside suchrange, or it may be responsive only totrafiic units proceeding in apredetermined direction.

It is well known that a body of magnetic ma- 25 terial when passedthrough a magnetic field will induce in a coil surrounding or adjacentto the field an electromotive force or voltage impulse. The passage ofthe magnetic body through the field momentarily provides a better paththan air for the magnetic fieldand accordingly the field is strengthenedand an induced electromotive force genera-ted in the coil. Manyarrangements utilizing the principle have been used'for detecting thepassage of vehicles in a roadway, as by 35 locating a coil and magnetadjacent to or under the pavement in the roadway. The impulse producedin a unit of this type may be used for governing operation of a warningsignal or bell, traffic signal, trafiic actuated signal controller, ga-40 rage door opening device or a counter for vehicles or other articlesgenerally, for example.

Many difierent types of impulse responsive devices may be employed inconnection with a magnet and coil unit of this type to control operation45 of the desired signal-operating device. For example, the impulseresponsive device may comprise a polarized relay, or highly sensitiverelay in series with a rectifier, or amplifier operating a relay, orother arrangement. A selective electri- 50 cal network may be used incooperation with the amplifier to give reliable operation of the relayupon the passage of vehicles and to make the detector vary substantiallynon-responsive to extraneous electrical and magnetic disturbancesassociated with nearby street railway or power lines.

The present invention contemplates a novel type of magnet and coil unitfor location in the traflic path for use with an impulse-responsivedevice. The novel magnet and coil assembly is inherently directional;that is, it produces upon 5 the passage of vehicles across the unit in apredetermined direction one type of impulse while for vehiclestraversing the unit in the opposite direction it produces a distinctlydifferent type of impulse. It is generally desirable however, to addcircuit arrangements shunting one of the coils to make the unit reliablyresponsive for unidirectional detection of high speed traffic. Also, byvirtue of its design,'the unit is inherently compensated to besubstantially non-responsive to extraneous magnetic disturbances at anyconsiderable distance from the detector or affecting the coils equally.The unit is additionally designed so that the effect of vehicles passingover any portion of the unit in the direction selected for controllingthe signalling is substantially uniform. Certain features of the designdisclosed .herein render the unit particularly reliable in detectingvehicles passing only within a sharply defined area in the selecteddirection at from very low to even the highest encounterable speeds. Yetit is substantially non-responsive to all other vehicles. This detectormay be adapted to be very substantially non-responsive to extraneouselectric and magnetic disturbances when not used as a uni-directionaldetector, and even when used as a uni-directional detector-retains to aconsiderable degree its non-responsiveness to such disturbances.

As the relay in the responsive unit is operated 5 only by impulsesproduced by vehicles travelling in the selected direction, the relayoperations are a highly accurate measure of the passage of vehicles inthe predetermined direction through the sharply-defined range of thedetector. As will 40 subsequently appear, the time duration of each suchrelay operation is roughly proportional inversely to the speed of theactuating vehicle.

It is an object of this invention to provide a detector of the magnetictype which will be responsive to units of traflic passing in a singlepredetermined direction.

It is also an object of the invention to provide a traflic detectordependably responsive to the passage of trafiic, and very substantiallynon-responsive to extraneous magnetic or electrical disturbances.

It is another object to provide a detector which will produce an impulsesubstantially uniform over the range, of the detector transverse to thetl'affic path for all vehicles passing over various parts of thedetector in one direction and not responsive to vehicles outside itsrange or to those passing over the detector in the opposite direction.

Another object of the invention is the provision of a traffic detectorof the magnetic type which will produce in a signalling circuit animpulse roughly proportional inversely to the speed of vehiclestraversing the detector in only a predetermined direction.

It is an additional object to provide a magnet and coil assembly whichupon the passage of traihe in one direction will produce a type ofvoltage wave adaptable to operate a signalling circuit and which uponpassage of traffic in the opposite direction will produce a voltage waveof different type or no wave at all so that traffic proceeding in thelatter direction will be ineffective to operate the signalling circuit.

Still another object of the invention is the provision of a magnet andcoil arrangement of this type for location in or adjacent to a trafficlane and including means for preventing false im pulses upon passage athigh speeds of vehicles proceeding in the wrong direction for detection.

Other objects will appear subsequently.

The invention will be described and its operation explained inconnection with the accompanying drawings illustrating a practicalembodiment, and in which drawings Figure 1 represents a preferred formof the magnet and coil assembly, located in a roadway, together with asignal and a control for same for operating the signal upon passage ofvehicles proceeding across the detector toward the signal;

Figure 2 is a vertical cross-sectional view along the line 22 of Figure1 and showing'the roadway and detector unit locatedbeneath the pavement;

Figure 3 is diagrammatic top View of the detector unit showing thewiring connections for the coils and the external connection to apolarized relay which serves as an illustrative type ofimpluse-responsive unit;

Figure 4 shows, another embodiment of impluse-responsive unit includinga relay and rectifier combination;

Figure 5 shows still another embodiment of impulse-responsivev unitcomprising an amplifier operating a relay; and

Figures 6 and '7 show alternative arrangements to that shown in Figure3.

Referring now to Figure 1, there is shown a roadway in which thedetector magnet and coil unit is located. The construction of apreferred form of the unit will more readily be apparent from Figures 2and 3 which represent respectively a cross-sectional view of the roadwayand magnetic unit and a view from directly above the unit looking downon it.

This roadway unit consists of a pair of magnetized iron bars I 0, II orbundles of iron rods having their axes spaced apart a short distance,for instance, about six or ten inches, each such bar or bundle beingencircled for part of its lengthby a coil assembly. The bars may havebeen given a permanent magnetism or may be maintained magnetized bysupplementary magnetizing means. The coil assembly on each bar is thesame and consists for each bar of two coils l2, I3 encircling the barand spaced apart at equal distances on either side of the mechanicalcenter of the bar. These two coils l2, l3 ace preerably connected inparallel with each other and both are in series opposition with a thirdcoil ll located with its electrical center at the mechanical center ofthe bar as shown. This centrally located coil I4 is a bucking coil whosepurpose will be explained below.

In practice it has been found expedient to assemble these three coilsinto a separate unit. Accordingly as shown in Figure 2, the coils havebeen placed on a cylindrical tube H: of non-magnetic material having anoutside diameter slightly less than the inside diameter of the coils,and an inside diameter great enough for the tube to slide freely on tothe bar or bundle of magnetized rods. Cylindrical shaped wedges T5 areprovided to hold the coils in proper relation with one another on thetube. A second cylindrical tube I1 is arranged to cover the entireassembly and at the ends of the unit the space between the tubes isclosed with washers l8, l9 and the space 20 surrounding the coilsbetween the inner and outertubes is filled with any suitable sealingcompound of insulating material. Any other suitable type of covering forthe coils may be used in lieu of the present arrangement to protect themfrom dampness or drainage water. The two leads 2|, 22 from the assemblyof coils are brought out through suitable holes in washer The twomagnetized bars with their encircling coil assembly units mounted onthem are located transversely of the vehicle lane or roadway with likepoles of the two magnets at the same end of the unit. As will beapparent from Figure 3 the two coil units 23, 24 are connected in seriesopposition by lead 2!, the lead 22 from one coil unit and thecorresponding lead'25 from the other coil assembly being connected tothe impulseresponsive unit. The bars may be held rigidly in place andthe coil assemblies protected from damage by casting in concrete orother nonmagnetic material as an additional precaution against damage bymoisture or abrasion.

As indicated in Figure 2, the magnetic unit may preferably be buried ashort distance below the road surface and the passage of a vehicleacross the detector will cause a considerable increase in the strengthof the field of the magnets, since the iron of the vehicle provides abetter magnetic path than air, through which the magnetic field circuitof each magnet was completed prior to the arrival of the vehicle.

By' well-known electrical law, in a simple coil linking a magnetic fieldthe flux change or change in intensity of the magnetic field induces avoltage in the coil, this voltage being proportional to the rate ofchange of flux linking the coil. The voltage generated is of onepolarity while the flux linking the coil is increasing; it is of theopposite polarity while this flux is decreasing, and when there is nochange in the flux linkages of the coil there is no generated voltage.For example, as a vehicle enters the detector field thus increasing theflux linking the coils, the voltage in any single coil increases in onedirection, during the brief instant the vehicle is momentarily over thedetector the voltage falls off to zero, and as the vehicle is leavingthe detector field decreasing the flux linking the coil, the generatedvoltage in the coil rises in the opposite direction.

As the voltage is proportional to the rate of change of the flux linkingthe coil and as this latter rate of change is dependent naturally on thespeed of the vehicle the voltages induced in the coil will be roughlyproportional in amount to the speed of actuating vehicles.

Not only will the voltage wave produced have a greater peak value withgreater speed but it will reach this peak value in less time and thusthe wave form for higher speeds of actuation will be characterized by awave front of greater steepness and frequency (if it were considered tobe repeated as a periodic oscillation instead of being transitory for asingle Vehicle) In the detector unit of the present invention the coilassembly on each magnet bar acts as a single coil. The use of twoparallel-connected coils spaced apart from the center on each barpermits of greater uniformity of voltage impulses by vehicles traversingany portion of the unit. If for instance, a vehicle passes over one co lthe field strength of this coil alone is increased and a voltage wavegenerated in this coil. If the vehicle passes centrally over the unitand causes an induced voltage to be generated in both coils the parallelconnection of the coils tends to make the peak voltage very nearly thesame as in the case of a vehicle passing at the same speed over only onecoil. However, in order further to insure that the induced voltage notbe greater for a vehicle passing over the central portion of thedetector than one passing near one end, the third coil l4 centrallylocated on the bar.is connected in series opposition with the twoparallel coils. Thus the voltage induced in coil l4 op poses the voltageinduced in coils l2. l3 and cuts down the height of the latter voltagewithout changing its wave form. The number of turns on this bucking coilis determined in accordance with the length of magnet bars and theamount of shielding provided by any magnetic portions of the housing ofthe detector structure to reduce the direct pickup of thiscoil thusattaining the desired uniformity of response over the entire length ofthe unit.

By loading the bucking coil M with a resistance 26 connected across itsterminals, it has been found that the direct pickup of this coil isfurther reduced. The bucking coil can thus be considered to act as ashading ring for flux try ng 1 to pass through the center point of themagnet bar, and serves to reduce the flux in the magnet linkin bothcoils and thus to flatten the curve of induced voltage for vehiclestravers ng anv portion of the detector. For a long slender mannet thefield pattern shows that all the ma net c field concentrated in thecenter of the bar does not continue entirely to the end of the bar. agreat portion of the flux leaving the sides of the magnet near the ends.Consequently. there is very little fanning out of the flux more than ashort distance beyond the ends of the magnet and the area through whichvehicles passing will actuate the detector accordingly has sharplydefined limits.

In order to obtain detection of vehicles passing over the detector in asingle predetermined direction, two magnets II), II and their associatedcoil assemblies, 23. 24 are arranged side by side with the magnet barsashort distance apart so that the magnetic fields overlap. A spacing offrom six to ten inches between the axes of the bars has been foundpracticable in the present embodiment; however, with magnets ofdifierent shape or with different coil arrangements other spacing may bedesirable. The unit coils 23 and 24 are connected in series oppositionas described and a condenser 21 is connected in shunt across the unitcoil on the side from which it is desired not to detect approachingvehicles, that is the coil nearer the intersection, as coil 24 in thepresent embodiment.

For vehicles travelling in the proper direction to be detected, as inthe direction indicated by the arrows in Figure 3, the induced voltagewave in each coil as hereinabove pointed out is first a voltage of onepolarity which rises to a peak and falls to zero, then rises to a peakin the opposite polarity and falls to zero. The wave induced in thesecond-coil 24 will be slightly displaced from the Wave of the firstcoil 23 in respect to time. Since in the present case, the second coilis in series opposition with the first, then accordingly the shape ofthe voltage wave across leads 22, 25 produced by a mass of iron movingin the proper direction for detection will be the difference between theimpulse waves in the two coils. Careful examination has shown this waveto consist of a small peak of one (minus) polarity, then a large peak ofthe second or opposite (plus) polarity followed by another small peak ofthe first (minus) polarity. In the absence of condenser 21, a vehicleproceeding in the opposite direction would produce a voltage wave havingfirst a small peak of plus polarity then a large minus peak and a smallplus peak. It is on the large peak of the second (plus) polarity,produced by a vehicle travelling in the proper direction for detectionthat the impulse responsive unit is arranged to operate the relay forsignalling purposes.

Due to the fact that the magnetic field of the detector induces eddycurrents in the axles and similar magnetic portions of the vehiclepassing over the detector, there is a slight time factor to beconsidered before the strengthening of the impulse wave is truly theresult of the substitution, in the magnetic field of the magnet, of thevehicles 'magnetic material for the air through which this field waspreviously completed. The presence of a condenser 21 or a resistanceacross the second coil 24 of the unit substantially retards the terminalvoltage across this coil from building up due to the effect of such eddycurrents or to the effect of the residual magnetism in portions of thevehicle. High speed vehicles which may move across the detector in thewrong direction for detecting without having been exposed to themagnetic field of the bars long enough to reverse their own magnetism,if their magnetism had previously been in the direction opposite to thatin the bars, are thus prevented from causing false voltages in thecoils.

currents the condenser required would be of high capacitance to produceany effect in delaying building up of the voltage. Furthermore, with thesame value of capacitance the condenser would act as a direct shortcircuit by-passto the higher frequency associated with a higher speedvehicle traversing the unit.

Values and space relations for the various parts which have been foundsuitable in one practical embodiment of the complete magnetic detectorroadway unit illustrated in Figs. 2 and 3 are as follows. The bars inand H may each be six feet long and about two inches in diameter forexample, made of permanent magnet iron and magnetized for a fieldstrength some fifteen to twenty times the earths magnetic field in ahorizontal plane about two feet over the bar, the latter distance beingabout in the middle of its working range.- The spacing of the two barsmay beabout seven inches between centers for example.

The end coils l2 and I3 may'for example be about three inches long andabout four inches in outside diameter and wound with some 14,000 turnsof wire to have a resistance of some 2500 ohms. The middle bucking coilmay for example be about four inches in outside diameter and about twoinches long, and wound with some 3750 turns of wire to have a resistanceof some 300 ohms. The loading resistance 26 may be 1000 to 2000 ohms.

The end coils I2 and I3 may be placed about two and'one half feet fromthe nearest end of the bar and the middle coil about in the center. Thecondenser 21 may be about ten microfarads, and the resistance of Fig. 6may be about three thousand ohms for example.

In general the complete magnetic unit may be placed in the roadway asshown in Figs. 1, 2 and 3 with the centers of the bars at a level aboutnine to ten inches below the road surface. The output-leads 22 and 25 ofthe magnetic unit may be suitably connected with a multi-stageelectronic amplifier of five thousand average gain and high impedanceinput. If a unit of eight foot length is employed for example instead ofthe six foot length the coil spacing from the center on each bar isincreased with the end coils again about two and one-half feet from theends of the bar.

It will be appreciated that the values, size and spacing described arelargely exemplary, and that they can be suitably proportioned by thoseskilled in the art to cooperate with various types of impulse responsivedevices. The spacing between the magnetized bars l0 and II is theprimary factor in obtaining uni-directional operation by providing theoverlapped magnetic fields, so long as the magnetic field of the bars isseveral times stronger than the earths natural magnetic field in theworking range above the unit. The condenser 21 is also a factor in thedirectional operation as described earlier in the specification. Thespacing of the individual coils along each bar is concerned primarilywith the uniformity of impulses obtained whether a vehicle passes overone end of the bar only or over the middle, and is significant whetherthe two A bar and coil assemblies are used in a directional orcompensated (against extraneous disturbances) magnetic unit or oneassembly is used individually as a simpler form of magnetic detectorwhere the directional and compensation features are not required.

The electrical values of the coils are related principally to thestrength and type of output impulse of the magnetic detector roadwayunit, however. Higher voltage output is obtained by increasing thenumber of turns and such output is adapted primarily to the electronicamplifier as an impulse responsive device, while a smaller number ofturns with lower resistance is adapted primarily to the polarized oralvanometer type relay.

The present type of unit is substantially nonresponsive to extraneouselectrical or magnetic disturbances due to the novel arrangement of thetwo magnets l0 and H and their associated coil assemblies 23, 24. Thecoil units 23 and 24 lie side by side as noted, spaced apart a shortdistance and connected in series opposition. A disturbance occurringmidway between the bars and coil units, that is, at any point on thecenter line between the bars and parallel to them, will aifect themagnetic field associated with each bar equally and a voltage of equalmagnitude will simultaneously be induced in each coil. The seriesopposition connection of the coils, however, if the effect of anyimpedance shunting one of the coil assemblies to unbalance their currentbuild-up characteristics is disregarded, will balance the voltagesagainst each other so that such disturbance will cause no impulse orresponse in output leads 22, 25.

Considering similar disturbances located at points not on theabove-mentioned center-line and at a distance from the detector, it willbe obvious that the distance of any of these disturbances from themagnetic field linking each coil assembly partially determines themagnitude of the induced voltage in the coil produced by thedisturbance. For disturbances occurring at any point off either end orside of the detector more than a very short distance from the detectorthe distance to both coils will be approximately equal, the inducedvoltages in the coils will be substantially the same, and the effect ofsuch extraneous disturbance on the terminal output of the detectoracross leads 22, 25 will therefore be substantially zero.

The presence of an impedance such as a condenser 21, or a resistance 43as shown in Fig. 6, across one of the coils in order to obtain improvedand reliable uni-directional detection will to a certain extent,depending upon the amount of unbalance of the coil units by suchimpedance, cut down the non-responsiveness of the detector to extraneousmagnetic conditions. Accordingly, it is generally desirable to determinein making an installation of this type whether the unit is to be highlycompensated against all extraneous magnetic disturbances, in which casethe coils are not shunted by impedances or are shunted by equalimpedances, or whether if vehicles travelling in either direction passdirectly over the unit-the unit must be made uni-directional. In thislatter case the coil on the side from which it is desired not to detectvehicles is shunted with a condenser 21 or a suitable sized resistance.However, even in such latter case experience indicates that about '75per cent of the compensating effect of the detector against extraneousdisturbances is retained when the coils are unbalanced to aiddirectional detection.

In practice a potentiometer 44 across output leads 22, 25 has been foundconvenient for producing varying degrees of unbalance between the coils.The moveable arm 45 of the potentiometer is connected to common lead 2|between the two coils. With such an arrangement complete vari ation ofthe amount of resistance shunting each coil in respect to the other isobtained by suitably adjusting the position of moveable arm 45. For

example, if it is desired to detect only vehicles approaching the coil23 side of the detector the arm 45 is moved to a point on potentiometer44 near the lead 22 end, so that a small resistance is placed acrosscoil unit 24 and a high resistance coil unit 23. The high resistance haslittle or no efi'ect on the voltage induced by the vehicle in coil unit23 but the low resistance shunt across coil unit 24 prevents thebuilding up in this coil of impulses by vehicles approaching in thewrong direction for detection. It will be appreciated that the form ofthe voltage impulse wave produced by the detector with the resistancesacross the coils, as shown in Figure 7, differs from that describedabove, and instead of comprising a small impulse followed by a largeimpulse in the opposite direction and then a small impulse in the firstdirection it now appears to lose one of the small impulses, probably thetrailing one, and increases the magnitude of the first two. Any of theimpulse responsive devices of Figures 3, 4 or 5, 'or others, may be usedwith the forms of the invention shown in Figures 3, 6 and 7.

The impulse responsive device for use with the magnetic unit may takeany of a number of forms. For example, a polarized relay of suflicientsensitivity to be actuated by voltages of this order of magnitude may beused, as shown in Figure 3. In such a case the coil of relay 30 issimply, connected directly across output leads 22, 25. Armature 3| isarranged to close against contact 32 when a voltage of plus polaritywhich is of sufiicient size, as caused by the passage of a vehicle inthe proper direction for detection, is applied to the polarized relay.The threshold value of impulse necessary to actuate thearmature is inexcess of the small voltages mentioned so that closure of armature 3|against contact 32 occurs only on the desired peak voltages of pluspolarity. A circuit completed through wires 33 and 34 by the contacts ofthe polarized relay may be arranged to operate a signal S of Figure 1directly or to energize an additional relay (not shown) with suificientcontact capacity for controlling the signal S, or other mechanism to beoperated.

In lieu of a polarized relay a sensitive relay 35 in series with arectifier as shown in Figure 4 may be used. The rectifier 36 is insertedin the circuit so as to prevent voltages of the minus polarity fromactuating the relay.

Ordinarily, however, with a magnetic detector of this general type ithas been found desirable in order to facilitate use of a relay ofsturdier construction, more reliable operating characteristics andgreater contact capacity, to amplify the voltage impulse from thedetector. A simple type of thermionic amplifier arrangement for thispurpose is shown diagrammatically in Figure for purpose of illustration.The impulse in output leads 22, 25 is impressed across the grid of tube40 so as to reduce, upon the passage of a vehicle across the street unitin the proper direction for detection, the negative grid bias normallysupplied from source 4|. The reduction in grid bias permits a greaterfiow of current in the plate-filament circuit to operate relay 42.

Vehicles passing in the wrong direction for detection do not actuate therelay sincethe tube is supplied with a grid bias near the cut-off pointof the plate current-grid voltage curve and small impulses of pluspolarity from the magnetic unit only slightly reduce the grid bias. Thenegative portion of the impulses increases the grid bias of the tube andof course reduces the current flowing in the plate circuit. Otherarrangements may be provided which include a selective electricalnetwork and one or more amplifiers of one or more stages, the selectivenetwork being adapted to reduce substantially or eliminate theextraneous impulses produced by trolley car lines, power wires and thelike since the latter impulses lie generally in a frequency range apartfrom the trafiic-produced detector impulses.

When two or more detector units as shown in Figure 1 are used to operatethe same relay, the output leads 22, 25 from each detector may beconnected together in parallel or series, care being taken that they beconnected in such a way to actuate the relay only upon the passage oftrafiic across each detector in the proper direction for detection.

The magnets in the detector unit need not necessarily be slender barmagnets as shown, but may be made in many other shapes. It is also to beappreciated that when the bar magnets are used the coils need notencircle the bars but may be located anywhere where each could be linkedby a substantial portion of its associated magnetic field.

Thus it will be seen that the present invention prov-ides a novelarrangement for detecting the passage of vehicles in a predetermineddirection in a roadway by generating an impulse of unique character forsuch vehicles which will cause suitable impulse responsive means tooperate a relay or other means for controlling signalling circuits. Fromthe foregoing description it will also be apparent that by virtue of thenovel magnet and coil arrangement the detector may be adapted to besubstantially non-responsive to extraneous electrical and magneticdisturbances; that the net period of closure of the output relaycontacts will be generally inversely proportional to the speed of theactuating vehicle; that the detector has a sharply-defined area ofsensitivity and that the response of the unit to vehicles passingthrough any portion of this area in the proper direction for detectionis substantially uniform, varying only with the speed and magneticcharacteristics of the vehicle; that compensating means form a part ofthe detector unit to reduce greatly the intensity of the impulses oftrafiic in the opposite or wrong direction for detection; and that whenused with a preferred form of responsive device the efiect of extraneousimpulses arising from stray disturbances as street car lines and powerwires, is minimized or eliminated.

It will be seen that the objects above enumerated and others areattained by applicants device. The form of the invention described andillustrated herein is to be considered as but one embodiment, and itwill be appreciated that many changes may be made in the construction ofthe unit or alterations in the design thereof or rearrangement of theparts, as the relative size, shape or location of the several coils, orother changes, without departing from the spirit of the invention asdefined by the claims.

I claim:

1. A traffic detector adapted to be located adjacent to a path oftraffic for detecting the passage of trafllc in such path, including incombination, means for producing two magnetic fields interlinking suchpath with the axes of magnetic polarity of such fields parallel andextending transversely to such path and spaced apart along the directionof such path, coils' located in such fields so as to have electromotiveforces generated in themselves upon the passage at any appreciabledistance from the coils will 76 produce substantially equal and oppositeimpulses of electromotive force in the coils and will producesubstantially no effect in said terminal leads but magnetic disturbancesresulting from the passage of such unit of traffic containing magneticmaterial along such path so as to effect the coils sequentially willproduce such opposing impulses sequentially so that separate impulsesacross said terminal leads will indicate passage of traiiic.

2. A trafilc detector adapted to be located adjacent to a path oftrafiic for detecting the passage of traffic in such path, including incombination, means for producing two magnetic fields interlinking suchpath with axes of magnetic polarity of such fields parallel and extendintransversely to such path and spaced apart along the direction of suchpath, coils located in such fields so as to have electromotive forcesgenerated in themselves upon the passage of any unit of trafliccontaining magnetic material in such path, and circuit means connectingthe said coils in series opposition and providing terminal leads forexternal connection, the coils and magnetic fields being arranged atsuch close spacing along the path of traffic-that the electromotiveforce generated in one of said coils will partially overlap and add tothe electromotive force generated in the other coil during the timewhile a unit of trafiic is passing over both coils, whereby a relativelylarge impulse of electromotive force of one polarity will be given bytraffic proceeding in one direction over the coils and a similar largeimpulse of electromotive force of the opposite polarity will be given bytraific proceeding in the opposite direction over the coils.

3. A magnetic type of traffic detector to be located adjacent to a pathof traflic for detecting the passage of trafiic in said path includingin combination, a pair of bars of magnetic material placed parallel toeach other adjacent to and transverse to the path of trafiic andmagnetized in the same direction to provide magnetic fields interlinkingsaid path, said bars being spaced relatively closely to each other alongsaid path, coils encircling the respective bars, and means connectingsaid coils in series opposition with each other and providing leads forexternal connection from the end of each coil whereby a unit of trafliccontaining magnetic material in traversing said trafllc path will firstinduce a voltage in one coil in one direction to produce a small voltageimpulse of one polarity across said leads and second, will inducevoltages in said one coil in the opposite direction and in the othercoil in said one direction and the voltages will be added together bythe series opposition connection of the coils to produce a large voltageimpulse of opposite polarity to the first impulse across the said leads,and then will induce a voltage in said other coil to produce anothersmall voltage impulse of the same polarity as the first impulse.

4. A magnetic type of trafllc detector to be located adjacent to a pathof traffic for detecting the passage of trafiic in said path includingin combination a pair of magnetized bars arranged parallel to each otheradjacent to the path of trafiic and extending transverse to such pathwith their magnetic polarity in the same direction, said bars beingspaced along such path relatively closely to each other as compared withthe length of the bars, a coil encircling each bar, and circuit meansconnecting the two coils .in series opposition to each other andproviding leads for external connection from one end of each coil,

the spacing of the coils and the connection of the coils being such thata relatively strong impulse of the electromotive force of one polaritywill be generated across said leads by the passage of a unit of trafilcin one direction along such path and a similar strong impulse ofopposite polarity will be generated by passage of a unit of traffic inthe opposite direction.

5. A magnetic type of traflic detector to be located adjacent to a pathof traific for detecting the passage of traffic in said path includingin combination a pair of magnetized bars arranged parallel to each otheradjacent to the path of traffic and extending transverse to such pathwith their magnetic polarity in the same direction, said bars beingspaced along such path relatively closely to each other as compared withthe length of the bars, a pair of coils connected in parallel in thesame direction on each bar, the two coils on each bar being placedrelatively near the ends of the bar, and circuit means connecting inseries opposition the two pairs of parallel connected coils andproviding leads for external connection from one end of the coils on onebar and the opposite end of the coils on the other bar.

6. A magnetic type of traffic detector to be located adjacent to a pathof trafilc for detecting the passage of traffic in said path includingin combination, a pair of magnetized bars placed parallel to each otheradjacent and transverse to such path with each bar having north andsouth magnetic poles and the two bars having their north magnetic polesin the same direction and said bars being spaced relatively closely toeach other along the path of traffic, a pair of coils encircling eachbar with the coils spaced near the opposite ends of the bar and saidcoils being wound in the same direction on said bar, circuits connectingthe south ends of the coils on one bar together and the north ends ofthe coils on said one bar together, and other circuits correspondinglyconnecting the south ends of the coils together and the north ends ofthe coils together on the other bar, another circuit connecting thesouth ends circuit of the coils on the first bar to the south endscircuit of the coils on the second bar, and leads for externalconnection extending from the respective north ends circuits of thecoils of the respective bars.

7. A tramc detector adapted to be located adjacent to a path of traflicfor detecting the passage of trafflc in such path and including incombination a bar of magnetic material placed in and transverse to thepath of trafilc and to provide a magnetic field interlinking said path,and a plurality of coils of wire encircling said bar and including onecoil located near each end of said bar, said coils being connected inparallel in the same direction electrically and having leads to permitexternal connection to the parallel connected coils, whereby said coilswill provide an electrical impulse across said leads in response to apassage of a unit of trafllc containing magnetic material along saidpath which impulse will have a substantially uniform value irrespectiveof the position of said traffic unit transverse to said path withrespect to said bar as long as a portion of said traflic unitpasess overa part of said bar.

8. A trafiic detector adapted to be located adjacent to a path oftrafilic for detecting the passage of trafllc in such path and includingin combination a bar of magnetic material placed in and transverseto thepath of traflic and magnetized to provide a magnetic field interlinkingsaid path, and a plurality of coils of wire encircling said bar andincluding one coil located near each end of said bar, and a thirdsmaller coil located substantially at the middle of said bar,

- and means connecting the end coils together in electrical parallelconnection and also connecting said third coil in series opposition tothe pair of parallel connected coils, and leads from the free end of theparallel connected coils and the opposite free end of the third coil forexternal connection of the entire coil assembly whereby a substantiallyuniform electrical impulse will be produced across said leads inresponse to the passage of a unit of traiiic containing magneticmaterial along said path irrespective of whether such unit of traflicpasses over either end or the middle of said bar.

9. A magnetic type of trafiic detector to be located adjacent to a pathof trafiic for detecting the passage of traffic in one direction onlyalong said path, including in combination, a pair of bars of magneticmaterial placed parallel to each other adjacent to and transverse tosuch path and magnetized in the same direction to provide magneticfields interlinking said path and said bars being spaced relativelyclosely to each other along such path, coils encircling the respectivebars, means connecting said coils on the two bars in series oppositionwith each other and providing leads for external connections from thefree end of each coil and an impedance connected in shunt with the coilon the second bar to be passed by traffic proceeding in said onedirection.

10. A trafiic detector of the character described in claim 9 in whichsaid impedance comprises a condenser.

11. A traffic detector of the character described in claim 9 in whichsuch impedance coinprises a resistance.

12. A magnetic type of traffic detector to be located adjacent to a pathof trafiic for detecting the passage of trafiic in one direction onlyalong said path, including in combination, a pair of bars of magneticmaterial placed parallel to each other adjacent to and transverse tosuch path and magnetized in the same direction to provide magneticfields interlinking said path and said bars being spaced relativelyclosely to each other along such path, coils encircling the respectivebars, means connecting said coils on the two bars in series oppositionwith each other and providing leads for external connection from thefree end of each coil, a resistance connected across said leads, and atapped connection extending from a point in the series connectionbetween said coils to a variable point on said resistance.

13. In a traffic detector of the magnetic type adapted to be locatedadjacent to a path of traffic for detecting the passage of traffic insuch path in one direction only, the combination of means for providingtwo closely adjacent magnetic fields interlinking said pathtransversely, coils located in respect to each of said magnetic fieldsso as to have generated in each coil a wave of electromotive force uponthe passage of any unit of traffic in said path, means connecting saidcoils in series opposition and including a lead from each coil forexternal connection, and means iiicluding an impedance shunting thesecond one of said coils which is passed by a unit of trafiic proceedingin said one direction to delay the generation of such electromotiveforce in the latter coil whereby difirent types of waves ofelectromotive force will be generated across said external leads bydifferent units of traffic passing said coils along said path inopposite directions.

14. In a traffic detector of the magnetic type adapted to be locatedadjacent to a path of traific for detecting the passage of traffic insuch path in one direction only, the combination of means for providingtwo closely adjacent magnetic fields interlinking said pathtransversely, coils located in respect to each of said magnetic fieldsso as to have generated in each coil a wave of electromotive force uponthe passage of any unit of traffic in said path, means connecting saidcoils in series opposition and including a lead from each coil forexternal connection, such coils and magnetic fields being located at,such spacing along the path of traffic that the waves of electromotiveforce in the respective coils will partially overlap eachother and theseries connection of the coils being such that such partially overlappedwaves will be added together in their overlapped portion to provide anincreased voltage across said leads, and means including an impedanceshunting the second one of said coils to be passed by trafir'cproceeding in said one direction along said path to delay the generationof the voltage wave in such secondcoil to increase such overlap andaddition of the voltage of the electromotive forces in said onedirection and to reduce such overlap and addition of voltage resultingfrom traffic proceeding in the opposite direction.

15. In a trafiic detector of the magnetic type for detecting the passageof traific in a trailic path, the combination of means for providing apair of closelyadjacent magnetic fields interlinking said pathtransversely, a coil placed in each of said fields for generating avoltage wave upon the passage of a unit of traffic containing magneticmaterial through such field, each of said coils having one end adaptedfor external connection and the other ends of the coils being connectedtogether, means including an impedance connected in shunt across one ofthe coils to retard the generation of a voltage wave in said one coilwhereby a unit of traffic passing the detector in one direction willproduce one type of voltage wavo across the external connection and aunit of traffic passing in the other direction will produce a differenttype of voltage wave.

16. In a device of the class described for use in the detection of aparamagnetic mass in substantially unidirectional linear motion, incombination, a pair of substantially identical electromagneticgenerators sequentially spaced in the direction of movement of the massand each generator including two termini, a conductor differentiallyserially connecting said generators to one another by attachment to twoI selected termini, a capacitor connected across the termini of saidgenerator which is last influenced by the said movement of theparamagnetic mass, the termini not connected by said conductor servingas means for connection of said generators to a circuit.

17. In a device for detection of a paramagnetic mass in substantiallyunidirectional motion, in combination, a pair of substantially identicalelectromagnetic generators, spaced sequentially in the direction ofmovement of the mass and each adapted to produce an impulse ofelectromotive force responsive to the passage of such mass, eachgenerator including-two termini and the remaining termini serving as ameans for connection of said generators to an external circuit, saidgenerators being so closely spaced that the impulses of electromotiveforce in the two generators partially overlap at said remaining terminias the mass passes the first generator and approaches the secondgenerator and the electromotive force produced in said first generatorwill add to the electromotive force produced in said second generator.

18. In a device for detection of a magnetized body in substantiallyunidirectional motion along a traflic path, in combination, a pair ofsubstantially identical coils closely spaced sequentially along saidpath, conducting means interconnecting said coils in series oppositionand providing a lead from each coil for external connection, and acapacitor connected in shunt with the coil last passed by said body inthe direction of said motion.

19. In a device for detection of road vehicles containing paramagneticmaterial in substantially unidirectional movement along a roadway in amagnetic field, -the combination of a pair of coils closely spacedsequentially along said roaclway in the direction of such movement,conductor means interconnecting said coils in series oppositionandproviding free ends for external connection, a paramagnetic core withineach of said coils, and a capacitor connected in shunt with the coillast passed by such vehicle in said movement.

for directionally detecting the passage of a magnetized unit of trafiicin such path, the combination of two coils spaced sequentially alongsaid path so as to have electromotive force generated in each coil uponthe passage of such traffic unit, conducting means interconnecting saidcoils in series opposition and including a conductor from each coil forexternal connection, said coils being so closely spaced that theelectromotive force generated in one coil as the traffic unit passessaid one coil and approaches the second coil will add to theelectromotive force generated in saidpsec- 0nd coil as traffic soapproaches the second coil so as to provide at the external connectionan increased impulse of electromotive force distinctive of the directionof passage of such trafiic unit.

21. In a traffic detector of the magnetic type adapted to be locatedadjacent to a path of traffic for directionally detecting the passage ofa magnetized unit of traflic in such path, the combination of two coilsspaced sequentially along said path so as to have electromotive forcegenerated ineach coil upon the passage of such trafiic Lmit,

conducting means interconnecting said coils in series opposition andincluding a conductor from each coil for external connection, and aparamagnetic core within each-of said coils, said coils being so closelyspaced that the electromotive force generated in one coil as the traflicunit passes said one coil and approaches the second coil will add to theelectromotive force generated in said second coil as traffic soapproaches the second coil so as to provide at the external connectionan increased impulse of electromotive force distinctive of the directionof passage of such traflic unit.

22. A traffic detector adapted to be placed close to a path of trafilcfor detecting the passage of a trafllc unit containing magnetic materialalong said path, comprising magnetic field generating means, a pair ofcoils disposed one behind the other along said path and linking themagnetic field so as to produce impulses of electromotive force in therespective coils responsive to passage of such trafiic unit, conductingmeans interconnecting said coils in series opposition and providing freeends from said coils for external connection, said coils being disposedso close to one another along said path that the opposing impulses ofelectromotive force in the coils so connected with overlap to produceacross the external connection an impulse of relatively large value ofone polarity by passage of such trafile unit in one direction and animpulse of relatively large value of opposite polarity by passage ofsuch traffic unit in the opposite direction.

23. A traflic detector adapted to be placed close to a path of trafilcfor detecting the passage of a trafiic unit containing magnetic materialalong said path, comprising means for producing a magnetic field intransverse direction to the trafllc path, at least two coils linking themagnetic field and spaced one from the other in said transversedirection, conducting means connecting said coils in parallel in thesame electromagnetic direction, and providing free ends for externalconnection, whereby the impulse of electromotive force produced at thefree ends of the coils by passage of such traflic unit is approximatelyuniform irrespective of the position of such traflic unit in saidtransverse direction.

24. A traific detector adapted to be placed close to a path of trafilcfor detecting the passage of a traffic unit containing magnetic materialalong said path, comprising magnetic field generating means, a .pair ofcoils disposed one behind the other along said path and linking themagnetic field so as to produce impulses of electro-motive force in therespective coils responsive to passage of such traillc unit, conductingmeans interconnecting said coils in opposition and providing free endsfrom said coils for external connection, said coils being disposed soclose to one another along said path that the opposing impulses ofelectromotive force in the cells so connected will overlap to produceacross the external connection an impulse of relatively large value ofone polarity by passage of such trafiic unit in one direction and animpulse of relatively large value of opposite polarity by passage ofsuch traflic unit in the opposite direction.

JOHN L. BARKER.

